Glossary · Control theory and process control
Integral controller
Also known as: I controller, Integral action, Reset action
German: I-Regler
In control engineering, an integral controller (integral action) produces an output proportional to the time integral of the control error, so it keeps changing its output until the steady-state error is zero.
- Control theory
In one sentence
Integral action integrates the control error over time and removes steady-state error, but adds phase lag and can cause windup.
Example
In a level loop, integral action slowly opens the outlet valve further until the level returns exactly to the setpoint after an increase in inflow.
How it applies
- Engineering: Integral action eliminates the steady-state offset that a pure Proportional controller leaves. It also adds phase lag and slows the loop, so it is usually combined with proportional action in a PI controller. Parameters are given as integral time, reset rate or integral gain, depending on the vendor.
- Commissioning: Too short an integral time causes slow oscillation; too long leaves the loop sluggish. Saturated actuators require Anti-windup.
- Documentation: Map vendor-specific parameter names and units (seconds, minutes, repeats per minute) in the terminology database, because mix-ups change the behavior by a factor of 60.
Integral controller vs. PI controller
The integral controller is the I component alone; it is slow and rarely used on its own. The PI controller combines it with proportional action and is the most common controller in process automation.